In case you get the following error when you connect to OpenVPN server from a Windows machine using OpenVPN-GUI, that means an error with your client side settings.
To solve this issue, try the following solutions,
1. Make sure OpenVPN-GUI runs with administrator privileges.
Close OpenVPN GUI from the system tray (bottom right hand side) >> Right click on OpenVPN GUI icon on the desktop >> Select “Run as Administrator”
2. Put the following directives to your OVPN file and run OpenVPN-GUI as administrator